The invention relates to a method of impregnating conductor bars for the stator winding of an electrical machine. The conductor bars are each provided on their surface with an insulation which is produced by wrapping each conductor bar with an insulating tape, preferably with a glass-containing or mica-containing insulating tape, which is impregnated with an insulating agent as impregnating fluid, preferably consisting of curable synthetic resin, in an impregnating tank in conjunction with an autoclave. The conductor bars are pressed to shape and size in a press die before the impregnating fluid cures.
It is conventionally known to provide the conductor bars for the stator winding of electrical machines with insulation before they are inserted into the stator slots provided for this purpose.
The insulation of the conductor bars conventionally consists of a wrapping with mica-containing insulating tape or of a mica tape which is impregnated with an impregnating fluid. The impregnating fluid is preferably a curable synthetic resin. It serves, on the one hand, for fixing the insulating wrapping and, on the other hand, for improving the insulation by preventing the possible absorption of moisture.
The impregnating agent is conventionally applied in a so-called impregnating tank which is arranged in an autoclave. First, a vacuum is thereby set for a short time in the autoclave. The establishment of the vacuum removes possible gas accumulations between the wrapping and the conductor bar which could constitute an obstacle to the absorption of the impregnating fluid.
For impregnation, the impregnating tank is then filled with the impregnating fluid and the respective conductor bar is dipped in. The bar is thereby wetted with the impregnating fluid. An overpressure is subsequently set in the autoclave, ensuring that the impregnating fluid penetrates into the insulating wrapping. Once it is ensured that all the cavities in the insulating wrapping are filled with impregnating fluid, ambient pressure is once more set in the autoclave and any excess impregnating fluid is returned to the supply container.
Due to the fact that the quantity of impregnating fluid necessary for flooding a conductor bar in the impregnating tank is about 10 to 50 times the quantity actually required for impregnating the conductor bar, and due to the fact that the excess which is necessary in each case is, if possible, to be reused, for example for the proper use of resources and in order to reduce the problem of disposing of synthetic resins of this kind, impregnation is to be carried out under defined conditions, for example at an appropriately low temperature which does not impair, or only insignificantly impairs, the stability of the resin, since the renewed processibility of the excess impregnating fluid is otherwise no longer guaranteed.
The viscosity of the impregnating fluid is therefore set in such a way that, on the one hand, thorough impregnation of the wrapping is ensured and, on the other hand, impregnating fluid no longer escapes during curing. After impregnation, that is to say after the wrapping has been impregnated with impregnating fluid, the curing of the impregnating fluid takes place, preferably at increased temperature, in order to reduce the curing time.
In view of the accuracy of contour and the dimensional accuracy required in the ready-to-install conductor bars, they are subjected before or during impregnation to pressing. This ensures that the cross sections of the conductor bars do not lead to fitting problems when they are being installed in the stator. This pressing may be carried out in various ways, specifically locally or totally and both at ambient temperature and at increased temperature, for example in a kiln. Also, if appropriate, pressing may be carried out, before impregnation, as so-called dry pressing, in contrast to so-called wet pressing which is carried out after impregnation has taken place. Before wet pressing, the conductor bar is wrapped in a separating foil which prevent the press die from adhering to the conductor bar.
Another important reason for pressing the insulation is, furthermore, to achieve optimum electrical and mechanical properties which depend essentially on the ratio of the fractions of impregnating fluid to mica or glass.
It follows from the foregoing that the impregnation process described above is highly complicated in manufacturing terms and therefore decidedly time-intensive.
It is accordingly an object of the invention to provide a method and device for impregnating conductor bars for the stator winding of an electrical machine, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which assures that, while a smaller quantity of impregnating fluid is required, the time necessary for impregnating a conductor bar is reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of impregnating a conductor bar for a stator winding of an electrical machine, which comprises:
providing a surface of a conductor bar with an insulation by wrapping the conductor bar with an insulating tape;
placing a pressure-tight and fluid-tight casing over an entire length of the conductor bar provided with the insulation to form an encased conductor bar;
subjecting the encased conductor bar on all sides to a pressure p1 in a pressing device and introducing an impregnating fluid into an interspace between the insulated conductor bar and the casing at a pressure p2 less than p1; and
pressing the conductor bar, loaded with impregnating fluid over the entire length thereof and surrounded by the casing, to shape and size in a press die at a curing temperature of the impregnating fluid.
In accordance with an added feature of the invention, the process is performed in an autoclave, i.e., the encased conductor bar is introduced into an autoclave at least prior to the subjecting step.
In accordance with an additional feature of the invention, the tape is mica-containing insulating tape and the impregnating fluid is a curable synthetic resin.
According to the invention, therefore, each conductor bar having a finished insulating wrapping is provided over its entire length with a pressure-tight and fluid-tight casing. In this context, the encased conductor bar is subjected on all sides to a pressure P1 in a pressing device, the impregnating fluid being introduced into the interspace between the insulated conductor bar and the casing at a pressure p2 less than p1, and the conductor bar, loaded with impregnating resin over its entire length in this way and surrounded by the casing, being pressed to shape and size at the curing temperature.
In comparison with the prior art processes, the method according to the invention improves both the outlay in terms of apparatus and the outlay in terms of process engineering considerably. Instead of impregnation in a bulky impregnating tank, the loading with impregnating fluid which takes place under pressure is now provided only within a casing resting comparatively closely against the conductor bar. This casing also at the same time functions as a separating foil, in order to prevent adhesion to the clamping jaws of a pressing device. In this case, in a development of the invention, the hose-like casing serving as a foil for separation from the pressing device is removed after curing has taken place, that is to say depending on the material used for the casing, being destroyed at the same time or in such a way that it can be reused.
The loading of the conductor bar with clamping jaws of a pressing device serves for ensuring the necessary accuracy of contour and dimensional accuracy during the operation of curing the impregnating fluid, whilst the intended pressing of the conductor bar may be accompanied by thermal action.
Particularly the latter-mentioned aspect has great potential for simplifying the method, since, due to curing in the press mould at increased temperature, on the one hand the original manufacturing time of approximately 50 h is markedly reduced to about one fifth of the time and, simultaneously, the accuracy of contour and the dimensional accuracy are improved considerably, this having a beneficial effect on the time required for mounting the conductor bars in the stator, since there is virtually no need for additional work for the purpose of achieving a fit.
In accordance with another feature of the invention, the conductor bar has a linear middle region and angled ends, and wherein the method comprises loading the linear middle region on all sides in a fixed pressing device having flexurally resistant clamping jaws and loading the angled ends with press jaws of a movable pressing device.
In accordance with a further feature of the invention, the introducing step comprises feeding the impregnating fluid at a relatively low temperature (e.g. room temperature) into the casing surrounding the conductor bar, and maintaining a fluid pressure of the impregnating fluid during the curing of the impregnating fluid.
In accordance with again a further feature of the invention, the impregnating fluid is cured at an increased temperature, such as at T greater than 90xc2x0 C.
With the above and other objects in view there is provided, in accordance with the invention, a device for performing the above-outlined method, i.e., a device for impregnating a conductor bar for a stator winding of an electrical machine, comprising:
an impregnating device having a hose-like flexible casing for receiving and encasing a conductor bar over an entire length thereof, wherein the conductor bar (10 is formed with a rectilinear region and angled regions adjoining the rectilinear region and is provided with an insulation;
a device communicating with the casing for filling the casing with pressurized impregnating fluid;
a pressing device with a stationary pressing device having a plurality of clamping jaws surrounding on all sides at least the rectilinear region of the conductor bar, and movable sleeve-like pressing devices surrounding and pressing the angled regions of the conductor bar adjoining the rectilinear region.
In accordance with yet an added feature of the invention, the sleeve-like pressing devices are formed by pressure hoses adapted to be laid around the ends of the respective conductor bar.
In accordance with yet an additional feature of the invention, the casing is a pressure-tight and fluid-tight casing with a cross section slightly larger than a cross section of the conductor bar wrapped with insulation. In the preferred embodiment of the invention, the casing is a shrinkable hose.
In accordance with a concomitant feature of the invention, the casing serves as a foil for separating the conductor bar from the clamping jaws of the pressing device, whereby the casing is removed after the impregnating fluid has cured.
According to an advantageous development of the method according to the invention, the conductor bar is loaded on all sides, in its linear middle region, in a fixed pressing device having flexurally resistant press jaws and, at its bent or angled ends, in each case by means of press jaws of a movable pressing device. With the aid of this procedure, laborious fitting work for accurate loading may be dispensed with.
In view of the curing of the impregnating fluid, it proves advantageous if the curing of the impregnating fluid takes place at increased temperature, preferably at T greater than 80xc2x0 C.
In a further preferred embodiment of the method according to the invention, the impregnating fluid is fed at low temperature, for example room temperature, into the casing surrounding the conductor bar, and the fluid pressure of the impregnating fluid is maintained during the curing of the latter.
A device for impregnating a conductor bar for a stator winding of an electrical machine by the method employed hitherto has an impregnating means, which receives the impregnating fluid intended for impregnating the conductor bar provided with an insulating tape, and a fixed pressing device with clamping jaws, into which the conductor bar can be at least partially inserted and in which it can be subjected to load.
The method according to the invention cannot be carried out directly by means of this device used hitherto, since, in this case, the impregnation of the insulation of the conductor bar takes place, for example, separately from the pressing which is subsequently carried out.
A further object of the invention is, therefore, to provide a device, by means of which the method according to the invention can be carried out and which, at the same time, has a correspondingly simple design, so that it is likewise simple to handle.
To achieve this object therefore, there is provision, according to the invention, for the impregnating means to be formed by a hose-like flexible casing which surrounds the conductor bar over the entire length of the latter, for providing a device for filling the hose-like casing with impregnating fluid which is put under pressure, for the clamping jaws of the fixed pressing device to surround on all sides at least the rectilinear region of the conductor bar, and for providing, in order to press the bent or angled regions of the conductor bar which adjoin its rectilinear region, in each case movable sleeve-like pressing devices which surround the conductor bar on all sides.
For simple handling, the sleeve-like pressing devices are formed by pressure hoses which are laid in each case around the ends of the respective conductor bar. These pressure hoses are to some extent flexible, so that they can be adapted to the dimensions of the conductor bars and, on the other hand, also fully load the conductor bar end regions deviating from the rectilinear.
In a further refinement of the invention, the hose-like casing is designed to be pressure-tight and fluid-tight and has a cross section which is slightly larger than the cross section of the conductor bar provided with the insulation, that is to say wrapped with the insulating tape. In this case, in a preferred development of the invention, the hose-like casing may be designed as a shrinkable hose.
Another advantageous feature of the device according to the invention is that the hose-like casing serves as a foil for separation from the pressing device and can be removed after curing has taken place. In this case, depending on the material used, there may be provision for the casing to be destroyed during removal. This makes it possible to free the conductor bar quickly. There may, however, also be provision for the casing to consist of a material not wettable by the impregnating agent or to be provided with a special coating, for example consisting of PTFE, so that, after non-destructive removal, it is possible for the casing to be reused.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for the impregnation of conductor bars for the stator winding of an electrical machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.